Optical imaging system

ABSTRACT

An optical imaging system includes five lenses in which a first lens includes a positive refractive power and a concave object-side surface, and a second lens includes a positive refractive power and a concave image-side surface. The first to fifth lenses are sequentially disposed from an object side to an image side.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit of priority under 35 USC § 119 to KoreanPatent Application No. 10-2016-0176315 filed on Dec. 22, 2016 in theKorean Intellectual Property Office, the disclosure of which isincorporated herein by reference in its entirety.

BACKGROUND 1. Field

The following description relates to an optical imaging system.

2. Description of Related Art

In general, camera modules are mounted in mobile communicationsterminals, computers, vehicles, a camera, a mobile device, or a tablet,enabling images of the surrounding environment to be captured.

In accordance with the trend for slimness of mobile communicationsterminals, camera modules have been required to have a small size andhigh image quality.

Further, camera modules for vehicles have also been required to have asmall size and high image quality to prevent obstruction of a driver'svisual field or negatively affect an appearance of a vehicle.

For instance, a camera used in a rearview mirror of the vehicle shouldbe able to capture a clear image in order to secure a view of a rearvisual field during vehicle operation, and is thus needs to have highimage quality.

In addition, a camera used in a vehicle needs to be able to clearlycapture an image of an object, even at night time in which illuminationis low. Therefore, a lens system that has a small size and captures animage in both a visible region and a near infrared region of the visiblespectrum is desirable.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

In accordance with an embodiment, there is provided an optical imagingsystem including: a first lens comprising a positive refractive powerand a concave object-side surface; a second lens comprising a positiverefractive power and a concave image-side surface; a third lens; afourth lens; and a fifth lens, wherein the first to fifth lenses may besequentially disposed from an object side to an image side.

Object-side surfaces and image-side surfaces of the first lens, thesecond lens, the third lens, and the fourth lens may be spherical, andan object-side surface and an image-side surface of the fifth lens maybe aspherical.

The first to fourth lenses may be formed of glass, and the fifth lensmay be formed of plastic.

The third lens may include a negative refractive power, a concaveobject-side surface, and a concave image-side surface.

The fourth lens may include a positive refractive power, a concaveobject-side surface, and a convex image-side surface.

The fifth lens may include a negative refractive power, a convexobject-side surface, and a concave image-side surface.

−6.5<{(1/f)*(Y/tan θ)−1}*100<−1.0 may be satisfied, where f may be anoverall focal length of the optical imaging system, Y may be half of adiagonal length of an imaging plane of an image sensor, and θ may behalf of a field of view (FOV) of the optical imaging system.

TTL/(2Y)<2.0 may be satisfied, where TTL may be a distance from theobject-side surface of the first lens to an imaging plane of an imagesensor and Y may be half of a diagonal length of the imaging plane ofthe image sensor.

−7.0<R1/f<5.0 may be satisfied, where R1 may be a radius of curvature ofthe object-side surface of the first lens and f may be an overall focallength of the optical imaging system.

−0.5<(R1+R2)/(R1−R2)<5.5 may be satisfied, where R1 may be a radius ofcurvature of the object-side surface of the first lens and R2 may be aradius of curvature of an image-side surface of the first lens.

0.1<f/f1<0.6 may be satisfied, where f may be an overall focal length ofthe optical imaging system and f1 may be a focal length of the firstlens.

1.5<f/EPD<2.4 may be satisfied, where f may be an overall focal lengthof the optical imaging system and EPD may be an entrance pupil diameterof the optical imaging system.

5.0<(T1+T2)/T3<12.0 may be satisfied, where T1 may be a thickness of thefirst lens, T2 may be a thickness of the second lens, and T3 may be athickness of the third lens.

v5<24 may be satisfied, where v5 may be an Abbe number of the fifthlens.

−2.5<f/f3<−1.0 may be satisfied, where f may be an overall focal lengthof the optical imaging system and f3 may be a focal length of the thirdlens.

An overall focal length f of the optical imaging system may be between7.0 mm to 7.5 mm.

A constant indicating brightness, Fno, of the optical imaging system maybe 2.22 or less.

A field of view of the optical imaging system may be between 43.51 ° to46.4°.

In accordance with an embodiment, there is provided an optical imagingsystem, including: a first lens comprising a positive refractive powerand a concave object-side surface; a second lens comprising a positiverefractive power; a third lens comprising a negative refractive power; afourth lens comprising a positive refractive power; and a fifth lenscomprising a negative refractive power, wherein the first to fifthlenses may be sequentially disposed from an object side to an imageside, and the fifth lens may be formed of plastic, and may include anaspherical object-side surface and an aspherical image-side surface.

The first to fourth lenses may be formed of a material having opticalcharacteristics different from a material of the fifth lens, andobject-side surfaces and image-side surfaces of the first to fourthlenses may be spherical.

Other features and aspects will be apparent from the following detaileddescription, the drawings, and the claims.

BRIEF DESCRIPTION OF DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 is a view illustrating an optical imaging system according to afirst embodiment;

FIG. 2 illustrates graphs of curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 1;

FIG. 3 is a table representing respective characteristics of lenses ofthe optical imaging system illustrated in FIG. 1;

FIG. 4 is a table representing aspherical coefficients of lenses of theoptical imaging system illustrated in FIG. 1;

FIG. 5 is a view illustrating an optical imaging system according to asecond embodiment;

FIG. 6 illustrates graphs of curves representing aberrationcharacteristics of the optical imaging system illustrated in FIG. 5;

FIG. 7 is a table representing respective characteristics of lenses ofthe optical imaging system illustrated in FIG. 5; and

FIG. 8 is a table representing aspherical coefficients of lenses of theoptical imaging system illustrated in FIG. 5.

Throughout the drawings and the detailed description, unless otherwisedescribed, the same drawing reference numerals will be understood torefer to the same elements, features, and structures. The relative sizeand depiction of these elements may be exaggerated for clarity,illustration, and convenience.

DETAILED DESCRIPTION

The following detailed description is provided to assist the reader ingaining a comprehensive understanding of the methods, apparatuses,and/or systems described herein. However, various changes,modifications, and equivalents of the methods, apparatuses, and/ormethods described herein will be apparent to one of ordinary skill inthe art. For example, the sequences of operations described herein aremerely examples, and are not limited to those set forth herein, but maybe changed as will be apparent to one of ordinary skill in the art, withthe exception of operations necessarily occurring in a certain order.Also, descriptions of functions and constructions that are well known toone of ordinary skill in the art may be omitted for increased clarityand conciseness.

Throughout the drawings and the detailed description, the same referencenumerals refer to the same elements. The drawings may not be to scale,and the relative size, proportions, and depiction of elements in thedrawings may be exaggerated for clarity, illustration, and convenience.

The features described herein may be embodied in different forms, andare not to be construed as being limited to the examples describedherein. Rather, the examples described herein have been provided so thatthis disclosure will be thorough and complete, and will convey the fullscope of the disclosure to one of ordinary skill in the art.

It will be apparent that though the terms first, second, third, etc. maybe used herein to describe various members, components, regions, layersand/or sections, these members, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one member, component, region, layer or section fromanother region, layer or section. Thus, a first member, component,region, layer or section discussed below could be termed a secondmember, component, region, layer or section without departing from theteachings of the embodiments.

Hereinafter, various embodiments will be described with reference toschematic views. In the drawings, for example, due to manufacturingtechniques and/or tolerances, modifications of the shape shown may beestimated. Thus, embodiments should not be construed as being limited tothe particular shapes of regions shown herein, for example, to include achange in shape results in manufacturing. The following embodiments mayalso be formed by one or a combination thereof.

In accordance with an embodiment, a first lens is a lens closest to anobject or a subject from which an image is captured. A fifth lens is alens closest to an image sensor or closest to an imaging plane.

In addition, a first surface of each lens refers to a surface thereofclosest to an object side (or an object-side surface) and a secondsurface of each lens refers to a surface thereof closest to an imageside (or an image-side surface). Further, all numerical values of radiiof curvature and thicknesses of lenses, Y (half of a diagonal length ofan imaging plane of the image sensor), and the like, are indicated inmillimeters (mm), and a field of view (FOV) of an optical imaging systemis indicated in degrees. In addition, in an embodiment, thicknesses andradii of curvatures of lenses are measured in relation to optical axesof the corresponding lenses.

Further, concerning shapes of the lenses, such shapes are represented inrelation to optical axes of the lenses. A surface of a lens being convexmeans that an optical axis portion of a corresponding surface is convex,and a surface of a lens being concave means that an optical axis portionof a corresponding surface is concave. Therefore, in a configuration inwhich one surface of a lens is described as being convex, an edgeportion of the lens may be concave. Likewise, in a configuration inwhich one surface of a lens is described as being concave, an edgeportion of the lens may be convex. In other words, a paraxial region ofa lens may be convex, while the remaining portion of the lens outsidethe paraxial region is either convex, concave, or flat. Further, aparaxial region of a lens may be concave, while the remaining portion ofthe lens outside the paraxial region is either convex, concave, or flat.

The paraxial region refers to a very narrow region in the vicinity of anoptical axis.

In accordance with an embodiment, an optical imaging system is describedin which an aberration improvement effect may be increased, a high levelof resolution may be implemented, an image may be captured even in anenvironment in which illumination is low, a field of view may be wide,and a deviation in resolution may be suppressed even in a wide change ina temperature.

An optical imaging system, according to various embodiments, may includefive lenses.

For example, the optical imaging system, according to the embodiments,may include a first lens, a second lens, a third lens, a fourth lens,and a fifth lens sequentially disposed from the object side. However, aperson of ordinary skill in the relevant art will appreciate that thenumber of lenses in the optical system may vary, for example, betweentwo to five lenses, while achieving the various results and benefitsdescribed hereinbelow.

The optical imaging system according to the embodiments is not limitedto only including five lenses, but may further include other components,if necessary. For example, the optical imaging system may furtherinclude an image sensor that converts an image of a subject incident onthe image sensor into an electrical signal. The image sensor isconfigured to capture an image of an object in a near infrared region aswell as a visible region. In addition, the optical imaging systemfurther includes a stop controlling an amount of light. For example, thestop is disposed between the second and third lenses.

In the optical imaging system, according to the embodiments, some of thefirst to fifth lenses may be formed of plastic or a polyurethanematerial, and others thereof may be formed of glass. In addition, thelenses formed of glass may have optical characteristics different fromthose of the lenses formed of plastic. For example, the first to fourthlenses may be formed of glass, and the fifth lens may be formed ofplastic.

In addition, in the optical imaging system, according to theembodiments, some of the first to fifth lenses may be spherical lenses,and others thereof may be aspherical lenses. In other embodiments, allof the first to fifth lenses may be spherical lenses, or all of thefirst to fifth lenses may be aspherical lenses.

As an example, first and second surfaces of the first lens, the secondlens, the third lens, and the fourth lens may be spherical, and thefifth lens may have at least one aspherical surface.

An aspherical surface of the fifth lens may be represented by thefollowing Equation 1:

$\begin{matrix}{Z = {\frac{{cY}^{2}}{1 + \sqrt{1 - {\left( {1 + K} \right)c^{2}Y^{2}}}} + {AY}^{4} + {BY}^{6} + {CY}^{8} + {DY}^{10} + {EY}^{12} + {FY}^{14} + {\ldots.}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In an example, c is a curvature (an inverse of a radius of curvature) ofa lens, K is a conic constant, and Y is a distance from a certain pointon an aspherical surface of the lens to an optical axis in a directionperpendicular to the optical axis. In addition, constants A to F areaspherical coefficients. In addition, Z is a distance between thecertain point on the aspherical surface of the lens at the distance Yand a tangential plane meeting the apex of the aspherical surface of thelens.

The optical imaging system including the first to fifth lenses may havea positive refractive power/a positive refractive power/a negativerefractive power/a positive refractive power/a negative refractive powersequentially from the object side towards the image side. However,although each lens is described with a particular refractive power, adifferent refractive power for at least one of the lenses may be used toachieve the intended result. For example, the first to fifth lenses mayhave a negative refractive power/a negative refractive power/a positiverefractive power/a negative refractive power/a positive refractive powersequentially from the object side towards the image side.

The optical imaging system, according to the embodiments, may satisfythe following Conditional Expression:

−6.5<{(1/f)*(Y/tan θ)−1}*100<−1.0   [Conditional Expression 1]

TTL/(2Y)<2.0   [Conditional Expression 2]

−7.0<R1/f<5.0   [Conditional Expression 3]

−0.5<(R1+R2)/(R1−R2)<5.5   [Conditional Expression 4]

0.1<f/f1<0.6   [Conditional Expression 5]

−2.5<f/f3<−1.0   [Conditional Expression 6]

1.5<f/EPD<2.4   [Conditional Expression 7]

5.0<(T1+T2)/T3<12.0   [Conditional Expression 8]

v5<24.   [Conditional Expression 9]

In an example, f is an overall focal length of the optical imagingsystem, Y is half of a diagonal length of an imaging plane of the imagesensor, θ is half of a field of view (FOV) of the optical imagingsystem, TTL is a distance from an object-side surface of the first lensto the imaging plane of the image sensor, R1 is a radius of curvature ofthe object-side surface of the first lens, R2 is a radius of curvatureof an image-side surface of the first lens, f1 is a focal length of thefirst lens, f3 is a focal length of the third lens, EPD is an entrancepupil diameter of the optical imaging system, T1 is a thickness of thefirst lens, T2 is a thickness of the second lens, T3 is a thickness ofthe third lens, and v5 is an Abbe number of the fifth lens.

Further, thicknesses of lenses refer to thicknesses thereof in aparaxial region or along an optical axis of the lenses.

Next, the first to fifth lenses forming the optical imaging system,according various embodiments, will be described.

The first lens has a positive refractive power. In addition, the firstlens has a meniscus shape of which the image-side surface is convex. Forinstance, a first surface (object-side surface) of the first lens isconcave in the paraxial region, and a second surface (image-sidesurface) thereof is convex in the paraxial region.

Both surfaces of the first lens are spherical.

The second lens has a positive refractive power. In addition, the secondlens has a meniscus shape of which an object-side surface is convex. Indetail, a first surface (object-side surface) of the second lens isconvex in the paraxial region, and a second surface (image-side surface)thereof is concave in the paraxial region.

Both surfaces of the second lens are spherical.

The third lens has a negative refractive power. Both surfaces of thethird lens are concave. In detail, first and second surfaces(object-side surface and image-side surface) of the third lens isconcave in the paraxial region.

Both surfaces of the third lens are spherical.

The fourth lens has a positive refractive power. In addition, the fourthlens has a meniscus shape of which an image-side surface is convex. Indetail, a first surface (object-side surface) of the fourth lens isconcave in the paraxial region, and a second surface (image-sidesurface) thereof is convex in the paraxial region.

Both surfaces of the fourth lens are spherical.

The fifth lens has a negative refractive power. In addition, the fifthlens has a meniscus shape of which an object-side surface is convex. Indetail, a first surface (object-side surface) of the fifth lens isconvex in the paraxial region, and a second surface (image-side surface)thereof is concave in the paraxial region.

At least one of the first and second surfaces of the fifth lens may beaspherical. For example, both surfaces of the fifth lens may beaspherical.

In the optical imaging system configured as described above, the firstto fifth lenses perform an aberration correction function to increaseaberration improvement performance.

In addition, the optical imaging system may have an Fno (a constantindicating brightness of the optical imaging system) of 2.22 or less to,thus, clearly capture an image of an object even in an environment inwhich illumination is low.

In addition, the optical imaging system may clearly capture the image ofthe object in both a visible region and a near infrared region of thevisible spectrum.

In addition, in the optical imaging system, according to theembodiments, the first to fourth lenses may be the spherical lenses, anda cost required for manufacturing the optical imaging system may, thus,be reduced.

In addition, in the optical imaging system, according to the embodiment,the first to fourth lenses may be formed of glass having a relativelylow coefficient of thermal expansion (CTE), such that a predeterminedlevel of resolution may be secured even in a temperature range of −40 to80° C. Therefore, the optical imaging system, according to theembodiment, may implement a high level of resolution even in anenvironment in which a change width in a temperature is large.

An optical imaging system, according to a first embodiment, will bedescribed with reference to FIGS. 1 through 4.

The optical imaging system, according to the first embodiment, includesan optical system including a first lens 110, a second lens 120, a thirdlens 130, a fourth lens 140, and a fifth lens 150, and further includesa stop ST and an image sensor 160.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses areillustrated in FIG. 3.

Also, an overall focal length f of the optical imaging system, accordingto the first embodiment, may be 7.5 mm, an Fno (a constant indicatingbrightness of the optical imaging system) thereof may be 2.22, and afield of view thereof may be 43.51°.

In the first embodiment, the first lens 110 has a positive refractivepower, and a first surface thereof is concave in the paraxial region anda second surface thereof is convex in the paraxial region.

The second lens 120 has a positive refractive power, and a first surfacethereof is convex in the paraxial region and a second surface thereof isconcave in the paraxial region.

The third lens 130 has a negative refractive power, and a first surfaceand a second surface thereof are concave in the paraxial region.

The fourth lens 140 has a positive refractive power, and a first surfacethereof is concave in the paraxial region and a second surface thereofis convex in the paraxial region.

The fifth lens 150 has a negative refractive power, and a first surfacethereof is convex in the paraxial region and a second surface thereof isconcave in the paraxial region.

Meanwhile, respective surfaces of the fifth lens 150 have asphericalcoefficients as illustrated in FIG. 4. For example, both of the firstand second surfaces of the fifth lens 150 are aspherical, and both ofthe first and second surfaces of the first lens 110, the second lens120, the third lens 130, and the fourth lens 140 are spherical.

In addition, the first to fourth lenses 110 to 140 are formed of glass,and the fifth lens 150 is formed of plastic.

In addition, the stop ST is disposed between the second lens 120 and thethird lens 130.

In addition, the optical imaging system configured as described abovehas aberration characteristics illustrated in FIG. 2.

An optical imaging system, according to a second embodiment, will bedescribed with reference to FIGS. 5 through 8.

The optical imaging system, according to the second embodiment, includesan optical system including a first lens 210, a second lens 220, a thirdlens 230, a fourth lens 240, and a fifth lens 250, and further includesa stop ST and an image sensor 260.

Respective characteristics (radii of curvature, thicknesses or distancesbetween lenses, refractive indices, and Abbe numbers) of lenses areillustrated in FIG. 7.

Also, an overall focal length f of the optical imaging system accordingto the second embodiment is 7.0 mm, an Fno (a constant indicatingbrightness of the optical imaging system) thereof is 2.06, and a fieldof view thereof is 46.4°.

In the second embodiment, the first lens 210 has a positive refractivepower, and a first surface thereof is concave in the paraxial region anda second surface thereof is convex in the paraxial region.

The second lens 220 has a positive refractive power, and a first surfacethereof is convex in the paraxial region and a second surface thereof isconcave in the paraxial region.

The third lens 230 has a negative refractive power, and a first surfaceand a second surface thereof are concave in the paraxial region.

The fourth lens 240 has a positive refractive power, and a first surfacethereof is concave in the paraxial region and a second surface thereofis convex in the paraxial region.

The fifth lens 250 has a negative refractive power, and a first surfacethereof is convex in the paraxial region and a second surface thereof isconcave in the paraxial region.

Further, respective surfaces of the fifth lens 250 may have asphericalcoefficients as illustrated in FIG. 8. For example, both of the firstand second surfaces of the fifth lens 250 are aspherical, and both ofthe first and second surfaces of the first lens 210, the second lens220, the third lens 230, and the fourth lens 240 are spherical.

In addition, the first to fourth lenses 210 to 240 are formed of glass,and the fifth lens 250 is formed of plastic.

In addition, the stop ST is disposed between the second lens 220 and thethird lens 230.

In addition, the optical imaging system configured as described abovemay have aberration characteristics illustrated in FIG. 6.

As set forth above, in the optical imaging systems, according to theembodiments, an aberration improvement effect is increased, a high levelof resolution is implemented, an image is captured even in anenvironment in which illumination is low, and a deviation in resolutionis suppressed even in a wide change in a temperature.

While this disclosure includes specific examples, it will be apparent toone of ordinary skill in the art that various changes in form anddetails may be made in these examples without departing from the spiritand scope of the claims and their equivalents. The examples describedherein are to be considered in a descriptive sense only, and not forpurposes of limitation. Descriptions of features or aspects in eachexample are to be considered as being applicable to similar features oraspects in other examples. Suitable results may be achieved if thedescribed techniques are performed in a different order, and/or ifcomponents in a described system, architecture, device, or circuit arecombined in a different manner and/or replaced or supplemented by othercomponents or their equivalents. Therefore, the scope of the disclosureis defined not by the detailed description, but by the claims and theirequivalents, and all variations within the scope of the claims and theirequivalents are to be construed as being included in the disclosure.

What is claimed is:
 1. An optical imaging system comprising: a firstlens comprising a positive refractive power and a concave object-sidesurface; a second lens comprising a positive refractive power and aconcave image-side surface; a third lens; a fourth lens; and a fifthlens, wherein the first to fifth lenses are sequentially disposed froman object side to an image side.
 2. The optical imaging system of claim1, wherein object-side surfaces and image-side surfaces of the firstlens, the second lens, the third lens, and the fourth lens arespherical, and an object-side surface and an image-side surface of thefifth lens are aspherical.
 3. The optical imaging system of claim 1,wherein the first to fourth lenses are formed of glass, and the fifthlens is formed of plastic.
 4. The optical imaging system of claim 1,wherein the third lens comprises a negative refractive power, a concaveobject-side surface, and a concave image-side surface.
 5. The opticalimaging system of claim 1, wherein the fourth lens comprises a positiverefractive power, a concave object-side surface, and a convex image-sidesurface.
 6. The optical imaging system of claim 1, wherein the fifthlens comprises a negative refractive power, a convex object-sidesurface, and a concave image-side surface.
 7. The optical imaging systemof claim 1, wherein −6.5<{(1/f)*(Y/tan θ)−1}*100<−1.0 is satisfied,where f is an overall focal length of the optical imaging system, Y ishalf of a diagonal length of an imaging plane of an image sensor, and θis half of a field of view (FOV) of the optical imaging system.
 8. Theoptical imaging system of claim 1, wherein TTL/(2Y)<2.0 is satisfied,where TTL is a distance from the object-side surface of the first lensto an imaging plane of an image sensor and Y is half of a diagonallength of the imaging plane of the image sensor.
 9. The optical imagingsystem of claim 1, wherein −7.0<R1/f<5.0 is satisfied, where R1 is aradius of curvature of the object-side surface of the first lens and fis an overall focal length of the optical imaging system.
 10. Theoptical imaging system of claim 1, wherein −0.5<(R1+R2)/(R1−R2) <5.5 issatisfied, where R1 is a radius of curvature of the object-side surfaceof the first lens and R2 is a radius of curvature of an image-sidesurface of the first lens.
 11. The optical imaging system of claim 1,wherein 0.1<f/f1<0.6 is satisfied, where f is an overall focal length ofthe optical imaging system and f1 is a focal length of the first lens.12. The optical imaging system of claim 1, wherein 1.5<f/EPD<2.4 issatisfied, where f is an overall focal length of the optical imagingsystem and EPD is an entrance pupil diameter of the optical imagingsystem.
 13. The optical imaging system of claim 1, wherein5.0<(T1+T2)/T3<12.0 is satisfied, where T1 is a thickness of the firstlens, T2 is a thickness of the second lens, and T3 is a thickness of thethird lens.
 14. The optical imaging system of claim 1, wherein v5<24 issatisfied, where v5 is an Abbe number of the fifth lens.
 15. The opticalimaging system of claim 1, wherein −2.5<f/f3<−1.0 is satisfied, where fis an overall focal length of the optical imaging system and f3 is afocal length of the third lens.
 16. The optical imaging system of claim1, wherein an overall focal length f of the optical imaging system isbetween 7.0 mm to 7.5 mm.
 17. The optical imaging system of claim 1,wherein a constant indicating brightness, Fno, of the optical imagingsystem is 2.22 or less.
 18. The optical imaging system of claim 1,wherein a field of view of the optical imaging system is between 43.51°to 46.4°.
 19. An optical imaging system, comprising: a first lenscomprising a positive refractive power and a concave object-sidesurface; a second lens comprising a positive refractive power; a thirdlens comprising a negative refractive power; a fourth lens comprising apositive refractive power; and a fifth lens comprising a negativerefractive power, wherein the first to fifth lenses are sequentiallydisposed from an object side to an image side, and the fifth lens isformed of plastic, and comprises an aspherical object-side surface andan aspherical image-side surface.
 20. The optical imaging system ofclaim 19, wherein the first to fourth lenses are formed of a materialhaving optical characteristics different from a material of the fifthlens, and object-side surfaces and image-side surfaces of the first tofourth lenses are spherical.